ABOARD A US MILITARY AIRCRAFT (AP) -- Defense Secretary Chuck Hagel said Wednesday it was not clear yet how many troops the U.S. will use to battle terrorists in Afghanistan in the coming two years, but he expressed some confidence that the Afghan forces will improve enough to secure and govern their own country.

In his first public comments about the drawdown plans unveiled by President Barack Obama this week, Hagel acknowledged there still were a lot of unanswered questions about how many of the nearly 10,000 U.S. forces remaining in the Afghanistan next year will be devoted to the counterterrorism mission. He said it also was unclear how many troops NATO and other international partners would contribute and what exactly those forces would do.

But he said he expected allies would make their decisions about the number and type of troops they would commit to the post-2014 mission in Afghanistan by the end of June. Hagel, who spoke to reporters traveling with him on a 12-day trip to Asia and Europe, expects to meet with NATO defense ministers next week.

President Barack Obama announced Tuesday that the U.S. would leave 9,800 U.S. troops in Afghanistan at the end of this year to continue training the Afghans and conduct counterterrorism missions. That number would be cut in half by the end of 2015, and most of the remainder would leave by the end of 2016.

Hagel said U.S. military commanders believe those numbers are adequate to train and advise the Afghans and fight terrorists. And while he said "there are no guarantees," he suggested the plans laid out by Obama were enough to keep Afghanistan from backsliding into more terrorist violence like what has happened in Iraq since U.S. troops left there.

The Afghan forces "are not yet where they need to be but the tremendous progress that has been made is significant," Hagel said.

Saying that the U.S. will be "living with terrorism for many years," Hagel added that terrorist networks are getting smarter, more sophisticated and interconnected around the world.

The two-year withdrawal plan for Afghanistan is contingent on the next Afghan president signing a security agreement with the U.S. Both candidates have said they would sign it.

The U.S. has said its troops would be located largely in the southern and eastern sections of Afghanistan, while German troops would take the lead in the north and Italian troops in the west.